Well, this is not exactly option 3, but here's how to completely hide the tight buttons - run netbeans with the -J-Dnb.tabs.suppressCloseButton key = true, for example,
[NetbeansDirectory] / bin / netbeans -J-Dnb.tabs.suppressCloseButton = true
Hope this helps ...
EDIT: NB 6.7.1 , , . -J-Dnetbeans.tab.close.button.enabled = false
EDIT2: